Japanese Patent Application Publication No. 2002-213306 describes an evaporated fuel processing device. The evaporated fuel processing device is provided with a canister configured to store fuel evaporated in a fuel tank, a control valve disposed on a purge passage communicating the canister and an intake passage, and a pump disposed on the purge passage. The evaporated fuel processing device drives the pump to discharge mixed gas (hereinbelow termed “purge gas”) containing the evaporated fuel in the canister and air to the intake passage through the purge passage.
In the evaporated fuel processing device, a quantity of fuel to be supplied to an engine is controlled by decreasing or stopping a flow rate from the pump when an air-fuel ratio is rich, and by increasing the flow rate from the pump when the air-fuel ratio is lean.